<template>
  <div class="pagination">
    <!-- 上 -->
    <button :disabled="pageNo == 1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)" :class="{active:pageNo == 1}">1</button>
    <button v-if="startNumAndEndNum.start > 2">···</button>

    <!-- 中间部分 -->
    <template v-for="(page,index) in startNumAndEndNum.end" >
       <button :key="index" v-if="page >= startNumAndEndNum.start" @click="$emit('getPageNo',page)" :class="{active:pageNo == page}">{{page}}</button>
    </template>

    <!-- 下 -->
    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)" :class="{active:pageNo == totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo == totalPage" @click="$emit('getPageNo',pageNo + 1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>
<script>
export default {
  name: "Pagination",
  props:['pageNo','pageSize','total','continues'],
  // 计算属性
  computed:{
    // 总共多少页
    totalPage(){
      return Math.ceil(this.total / this.pageSize)
    },
    // 计算出连续的页码的起始的数字与结束的数字[连续的页码数字:至少是5]
    startNumAndEndNum(){
      const {continues,pageNo,totalPage} = this
      // 先定义两个变量存储起始数字与结束数字
      let start = 0
      let end = 0
      // 连续页码数字5【就是至少得有5页】，
      // 如果出现不正常的现象【就是总页数不够5页】
      if(continues > totalPage){
        start = 1
        end = totalPage
      }else{
        // 正常现象【总页数大于5页】不能写死直接 - 2，因为有可能连续页变化
        // 例子：当前第8页，连续页码5: 6 7 8 9 10
        // 例子: 当前第8页 连续页码7： 5 6 7 8 9 10 11
        // 起始数字
        start = pageNo - parseInt(continues / 2)
        // 结束数字
        end = pageNo + parseInt(continues / 2)
        // 把出现不正常的现象【start数字有0和负数】纠正
        if(start < 1){
          start = 1
          end = continues
        }
        // 把出现不正常的现象【end页数大于总页数】纠正
        if(end > totalPage){
          end = totalPage
          start = totalPage - continues + 1
        }
      }
      return {start,end}
    }
  }
};
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
.active{
  background-color: skyblue;
}
</style>
